Important note: Requires an additional Energy Rejection Filter (D-ERF) in front of the lens. SolarSpectrum Filter are not available by shopping cart system and have sometimes long waiting periods. If you are interested, please contact us by email or contact form

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Can I use an UV/IR-Cut filter or the BBHS mirror in front of an H-Alpha or Calcium Solar Filter? Do you recommend the 2" BBHS or 2" Clicklock Mirror for solar observation?

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Question by: Enrique V. on Sep 26, 2016 3:04:00 PM | 1 Answer(s)

If you want to observe the sun in H-Alpha, we recommend the standard dielectrical Clicklock mirror (# 2956100) in combination with a suitable filter combination, because the dielectrical filter reflects less radiation below 380nm and above 740nm. This way, the mirror can reduce the strain on the following filters at least a little bit.Please do also use an energy rejection filter in front of the telescope to reduce the strain on the filters as much as possible.

We highly advise against visual calcium observations of the sun - the 397nm of Calcium are already ultraviolet radiation, and UV-radiation can cause phototoxic reactions which can harm your eyes. In addition, even young people can't see these wavelengths very good, and sensitivity decreases with the age. Because of this, the eye doesn't feel if the intensity is much too high. If you now try to increase the amount of radiation (e.g. with another mirror) to achieve a brighter image, you will increase the risk for eye damage. According to the newest norms for eye safety and to ophtalmologist conclusions, the sun must not be observed visualy at 397nm.

We highly advise to only observe the sun in calcium photographically, then you also do not need a star diagonal. We can't understand why some manufacturers promote these calcium-filters for visual observations.

We also advise against placing a filter so close to the focus - any energy rejection filter belongs in front of the front lens, even if this sets high demands to the quality of such a large filter. Placing the filter close to the focus will save money, because you can use a much smaller filter, be we absolutely can't recommend it - because of our own conscience as well as because of EU-regulations. The filter would receive all the energy collected by the front lens. We can only recommend putting the energy rejection in front of the front lens, which is the ethically and technically correct method.

Related Articles

An experience and observation report on the new Baader Telecentric System TZ-3 and the Research Grade (RG) Telecom­pressor (TC) 0.4 for solar observation in the H-alpha light with SolarSpectrum filters
download the complete review (pdf)
Introduction
Successful H-alpha-observations of the sun with narrow-band line filters from the manufacturers “SolarSpectrum” and / or "DayStar" require an almost parallel beam of light with a focal ratio of approx. f/30 directly in front of the filter, otherwise the filter will not work properly. This is not so easy with today's fast optical systems, which work around f/7. Such an opening ratio can be achieved either by masking (reducing) the front lens opening or by parallizing the optical beam with a "telecentric system" (TZ). * TZ: See also the supplement at the end of the report.
My "solar telescope" is an AstroPhysics refractor with an aperture of 155mm and a focal length of 1.085mm, the aperture ratio in the prime focus is f/7.
In order to use the filter without extending the focal length, the telescope's aperture would have to be reduced to approx. 35mm in order to realize the optimum f/30 focal ratio. It is clear that this is highly unsatisfactory – the resolution detail...

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